The blacklisting of al-Nusra — which makes up about nine per cent of opposition forces — was met by swift backlash as both Syrian Islamists and nonviolent activists perceived the move as an attempt by the U.S. to manipulate the outcome of the 21-month-conflict.

The U.S. admitted as much, saying that the move is “intended to expose them” because the group’s “extremist ideology has no role in a post-Assad Syria.”

Al-Nusra aims to create an Islamic state in Syria ruled by strict Sunni Islamists and has vowed to fight any secular government.

An Iraqi who joined the Free Syrian Army (FSA) told The New York Times that there will be so many battles between” rebel groups after Assad falls and that forces “will unite against al-Nusra.”